Scientific information forming a portion of the basis for an understanding of the present invention has been developed over a significant period of time, in excess of 100 years. The prior art developed over that period of time is accordingly discussed in detail in order to assure its proper understanding in connection with the present invention and to assure a better understanding of the novel contribution of the present invention over the substantial body of prior art described below.
Inulin was first discovered in 1804 by separating the juice extracts from the Jerusalem artichoke and crystallizing or purifying the inulin from this juice. Being analogous to starch which is a glucose polymer, inulin is chiefly a fructose polymer. While starch is the primary storage carbohydrate in almost all grains and tubers (such as potatoes), inulin is the primary storage carbohydrate in the tubers of the dahlia (Dahlia variablis) and other members of the Compositae family, notably the Jerusalem artichoke (Helianthus tuberosus), and is found in the roots of elecampane (Inula Ilenium), dandelion, chicory, and salsify.
Analysis by Praznick.sup.1 of the crude inulin obtained from these sources without purification revealed chains of varying length depending upon the source (see Table 1). He also noted that the range and distribution of the polymers was dependent not only on the source, but on the time of year that the sample was obtained as well. Tubers harvested in the fall immediately after a killing frost had longer polymers than tubers harvested in the early spring.
TABLE 1 ______________________________________ Polymer Distribution of Crude and Purified Inulin Obtained from Jerusalem Artichoke, Dahlia and Chicory Polymer Distribution (DP Range) Inulin Source (2-19) (20-40) &gt;40 ______________________________________ Jerusalem artichoke 74 20 6 Jerusalem artichoke purified 2 24 76 Dahlia 31 21 40 Dahlia purified 5 30 65 Chicory 55 18 17 Chicory purified -- -- -- ______________________________________
Jackson.sup.2 reported that purification of the inulin by recrystallization from water produced a uniform product (which was hot water soluble) irrespective of the source. This agrees with the much later findings of Praznick summarized in Table 1.
The general method for the commercial preparation of inulin, as described by E. McDonald.sup.3 of the National Bureau of Standards, involved hot water extraction of plants rich in inulin followed by the addition of milk of lime prior to filtration and precipitation of the inulin. The inulin was then recrystallized to make a purified inulin product.
The physical properties of inulin according to the Merck Index (#4872) published by Merck & Co., Rahway, N.J. include an average molecular weight of about 5,000 and solubility in hot water with very slight solubility in cold water. The USP (United States Pharmacopoeia) lists the standards for inulin which include a residue on ignition (ash) of not more than 0.05% and a completeness of solution including clarity.
Purified inulin has been utilized in the past in determination of Glomerular Filtration Rates (GFR), permeability studies (as an extracellular marker), and hydrolytic studies with regard to the commercial production of fructose from inulin. To date, the usage of inulin has been limited to purified inulin and its subsequent use as a diagnostic chemical. There has been no commercial usage of purified inulin as a therapeutic or supplementary food material, presumably due to the high cost of purified inulin. A recent proposed usage of inulin is as a fat replacer. By utilizing the fact that a 20% solution of inulin sets into a hard "pudding-like" texture having the smooth feel of fat, it was suggested that this be used in baking to replace fat.
The literature has described numerous processes for the ultimate preparation of purified inulin. A notable and unique exception is the reference by Mitchell, et al..sup.4, who taught the preparation of a "crude" form of inulin which had economical benefits making it feasible for consideration as a human food material. "Crude" inulin as described by Mitchell has not been purified by recrystallization. Instead, the "crude" inulin of Mitchell is precipitated from the original juices and therefore contains some of the nutrients found in the juice. This "crude" inulin, like purified inulin, has been precipitated from an aqueous solution and has the similar property of being soluble only in hot water.
Mitchell teaches that inulin as it exists in the tuber is in a soluble state. By immediately pressing the comminuted tuber, the majority of the inulin can be removed from the plant resulting in a juice rich in inulin. Subsequent cooling of the pressed inulin juice results in the precipitation of the desired "crude" inulin. Mitchell warns that if pressing is not performed immediately, the inulin begins to precipitate and separation of the inulin from the plant material becomes very difficult requiring hot water to solubilize and extract the majority of the inulin.
The solubility of inulin has never been well understood. The differences in the solubility of inulin have been described by McDonald.sup.3, C. F. Phelps.sup.5, and R. Hill.sup.6. In general, Phelps found that recrystallized inulin did not obey the phase rule and increased in solubility between 60.degree. C. and 100.degree. C. Phelps hypothesized that a change in structure or polymorphism occurred (as opposed to a change in polydispersity). McDonald described the different forms of inulin according to how they dissolved in water. The unstable beta form, obtained by recrystallization from alcohol, was considered more soluble and dissolved in cold water while the alpha form was more insoluble and dissolved only in hot water. Most importantly, upon standing, the more soluble beta form changed to the more insoluble alpha form.
R. Hill reported solubility of inulin based on polymer size. Hill revealed that fructose polymers having a DP value of less than approximately 15 (average MW=2500) were soluble in 20.degree. C. water while those fructose polymers of about DP 33 were insoluble.
Importantly, it should be noted here that inulin of DP 8 and higher if precipitated from an aqueous solution, results in an inulin polymer which is not cold water soluble. Hill, who used said hydrolysis on purified inulin to degrade the polymers, believed that the shorter polymers (DP of less than 15) were inherently cold water soluble. This conclusion is questioned in consideration of the fact that Hill recrystallized these shorter polymers from alcohol. McDonald taught that a cold water soluble polymer of inulin could be formed by recrystallization from alcohol. Consequently, it is believed that Hill mistakenly attributed cold water solubility as a function exclusively of polymer size instead of polymorphism. In any case, Hill went on to show that the former polymers were readily hydrolyzed in acid (PH=1, 37.degree. C. for one hour) while the latter were not hydrolyzed under identical conditions. Hill concurred with the popular belief that, in order for inulin to be metabolized by humans, it first had to be hydrolyzed by gastric acids to fructose, the fructose subsequently being absorbed and utilized according to this hypothesis. Hill taught that the hydrolysis of purified inulin to smaller polymers of less than DP 15 formed a product best suited for human consumption.
The tubers of the Jerusalem artichoke and the dahlia have been eaten by different cultures throughout history. However, they were never found to be very popular. The Heliamhae tribe of the Compositae family which includes the Jerusalem artichoke and the dahlia have been reposed to cause dermatitis.sup.7. The major sensitizing agents were found to be the sesquiterpene lactones. Patch test reactions to Compositae plants in sensitized individuals are frequently severe, vesicular or bullous, and persistent. In considering a non-purified inulin as a food material, the sensitivity that some individuals have to the Compositae family would be cause for concern.
With regard to the crude pressed juices from dahlia tubers, Jerusalem artichoke and chicory, the polymer distribution of the inulin found in these sources is significant. Before recrystallization, the polymer distribution of chicory and the Jerusalem artichoke show high levels of the smaller chains and relatively low levels of the high molecular weight polymers relative to dahlia inulin. Most of the current literature with regard to inulin refers to the Jerusalem artichoke and chicory due to the established agricultural availability of these sources. References given for dahlias are solely in regard to their consideration as an ornamental plant. Earlier work had already established dahlias as the best source of inulin but, since dahlias were not grown commercially except for ornamental purposes and the market for purified inulin was limited, the Jerusalem artichoke and chicory almost exclusively filled the world's need for purified inulin.
During the time from 1976-1992, considerable work has been reported in the literature with the Jerusalem artichoke as the general subject. Uses of the Jerusalem artichoke have been summarized in a review article by N. Kosaric, et al..sup.8 in 1985. The primary uses included food, fodder, alcohol production and high fructose syrup production. Most of the literature pertaining to the Jerusalem artichoke, though, concerns hydrolysis (of the inulin) and fructose production.
Literature regarding chicory yields information primarily in the area of coffee additive material as well as hydrolysis of the inulin to produce fructose for use as a sweetener.
Recent literature has revealed information which suggests the beneficial effects of Bifidus bacteria in the human gut. The Japanese have reported that fructo-oligiosaccharides up to DP=4, which have been synthesized from sucrose, are well utilized by Bifidus bacteria and have been used to promote Bifidus cultures in the gut.
Comparative feeding studies involving purified inulin, whole baked Jerusalem artichokes and fructose were performed by many researchers in the period from 1870 to shortly after the discovery of insulin. Root and Baker.sup.9 in 1925, reported that all three substances appeared to be utilized. Blood glucose levels were found to increase the greatest with fructose and the least with purified inulin. Also it was found that the maximal respiratory quotient after ingestion of Jerusalem artichokes or inulin occurred in 2-6 hours as compared with less than two hours for fructose. Another very important finding by Root and Baker was that during the experimental days when insulin was removed from the diabetic patients, the tendency towards acidosis was counteracted by all three substances.
It was then concluded that inulin, particularly that found in the Jerusalem artichoke, was a carbohydrate that could well be tolerated by diabetics. Fructose was assumed to be the key factor responsible for the prevention of ketoacidosis in diabetics, and hence later gained recognition as the "diabetic sugar". The other advantages were attributed to a slow rate of gastric hydrolysis of the inulin followed by absorption of fructose. The soluble fiber pectin, found in the Jerusalem artichoke, was also considered to contribute to the slow absorption rate of the fructose thus preventing sharp blood glucose rises. Based on these findings, many early diabetic physicians including Root and Baker proposed the usage of inulin-containing vegetables in the diet of diabetics. Unfortunately, because of the unavailability of the tubers (potatoes) requiring drying and storage so that the individual could have a year-round supply, the large amounts required (40 to 500 grams, or one to two potatoes daily), the singularity in available form, and the recent discovery of insulin, this idea was considered impractical.
Feeding studies involving a purified inulin showed that consumption resulted in the production of large amounts of intestinal gas. Because glomerular filtration studies performed by Miller, et al..sup.10 showed that purified inulin was neither excreted nor absorbed by the renal tubules, it was generally assumed that purified inulin was not readily metabolized.
It is not surprising that the Jerusalem artichoke, with its polymer distribution favoring small molecular weight species, was found by Root and Baker to be well utilized as a food. The inulin polymers (later found by Praznick and others to be less than DP 10) would readily be hydrolyzed to fructose in the stomach acids and utilized as such. While it was possible to explain some of the advantages noted upon feeding purified inulin and Jerusalem artichoke by hydrolysis of inulin followed by absorption of fructose, this explanation was not totally satisfactory.
A research paper by H. B. Lewis.sup.11 reviewed the thinking at the time (1912) with regard to the value of inulin as a foodstuff. He basically summarized the work of Miura and Mendel and Nakaseko which showed that, even under the most favorable conditions, little glycogen was formed in rabbits after feeding inulin. Since the formation of glycogen occurs rapidly after the feeding of fructose, the above researchers concluded a lack of assimilation of inulin. Lewis also stated that the results of Neubauer's work also supported the idea that inulin was not hydrolyzed to fructose. In a case of fructosuria Neubauer found no increase in the fructose content of the urine after feeding 80 grams of inulin. No inulin was found in the feces either. It was observed however, that the patient suffered from intestinal gas formation after the consumption of the inulin. It was concluded that inulin was not hydrolyzed to fructose and in fact not utilized thereby producing the observed gas formation. Lewis also pointed to the work of DuCamp who explained the absence of inulin in the feces by suggesting that B. coli communis and other intestinal bacteria decompose inulin without any production of sugar.
Overall, the results of all of the research concerned with the consumption of inulin indicated a paradox. Some feeding studies found inulin to be well utilized and assumed it to be hydrolyzed and metabolized as fructose while other results indicated that inulin could not be hydrolyzed and then metabolized as fructose. A suitable explanation that would encompass the results of all these research studies was never found.
Looking at more recent developments in carbohydrate metabolism during the past decade, phosphofructokinase has been considered the key regulatory enzyme in glycolysis and hence carbohydrate metabolism. According to a recent review by Louis Hue and Ramoff Bartrons.sup.12, one of the most important and potent stimulators of this enzyme is fructose 2,6-bisphosphate which is made in vivo by the action of the enzyme phosphofructo-2-kinase on fructose-6-phosphate. It was shown that glucagon promotes glycogenolysis and yet inhibits glycolysis by suppressing the production of fructose 2,6-bisphosphate. Insulin acts to suppress the action of glucagon but does not actually activate the production of fructose 2,6-bisphosphate and hence glycolysis. In agreement, Simon Pilkis.sup.13 in recent years found that certain carbohydrate disorders, such as diabetes mellitus, exhibit a lower than normal concentration of fructose 2,6-bisphosphate and thus an impairment of the efficient utilization of carbohydrates via glycolysis.
It was also known that disorders of carbohydrate metabolism such as diabetes, which result in the inefficiency to utilize carbohydrates, can cause other health problems.sup.14. These problems include vascular micro- and macro-angiopathies which manifest themselves as nephropathy, retinopathy, coronary artery disease, cerebral vascular disease, and peripheral vascular disease.
Overall, the prior art understanding of inulin describes a stable hot water soluble polymorphic form when recyrstallized or precipitated from aqueous solutions and an unstable cold water soluble polymorphic form when the inulin is recrystallized from alcohol. The latter polymorphic form readily converts to the hot water soluble polymorphic form upon standing. Studies to determine the metabolism of inulin have been performed either with the hot water soluble polymorphic form or whole Jerusalem artichokes. It was commonly understood that the natural flora of the human digestive tract did not possess enzymes suitable for hydrolyzing the inulin in the stomach or intestines. It was further believed that acid hydrolysis could occur to some extent but only on those polymers of less than about DP 10. Consequently, Jerusalem artichokes which have a polymer distribution predominantly in the range of less than DP 10 could be well utilized while purified inulin could not (unless first subjected to hydrolysis to fructose).